[IDV #FAY-719487]: Albers Conical Equal Area netCDF

Hi Tyn-

> On Wed, 2008-03-05 at 08:08 -0700, Unidata IDV Support wrote:
> > Hi Tyn-
> 
> > You'd need something like the following:
> >
> >    char Albers_Projection;
> >      :grid_mapping_name = "albers_conical_equal_area";
> >      :standard_parallel = 20.0, 60.0;
> >      :longitude_of_central_meridian = -32.0;
> >      :latitude_of_projection_origin = 40.0;
> >      :false_easting = 0.0;
> >      :false_northing = 0.0;
> >      :_CoordinateTransformType = "Projection";
> >      :_CoordinateAxisTypes = "GeoX GeoY";
> >
> > and for projection_x_coordinate and projection_y_coordinate, you'd need to 
> > add:
> >
> >
> > <attribute name="_CoordinateAxisType" type="String" value="GeoX" />
> >
> > <attribute name="_CoordinateAxisType" type="String" value="GeoY" />
> >
> 
> 
> O.k, this is what i came up with after your suggestions:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2"; 
> location="dods://iridl.ldeo.columbia.edu/SOURCES/.USGS/.ADDS/.NDVI/.NDVIrg/.dekadal/.maximum/.NDVI/dods"
>  >
> <attribute name="title" type="String" value="NDVI" />
> <variable name="x" shape="x" type="double">
> <attribute name="units" type="String" value="m" />
> <attribute name="_CoordinateAxisType" type="String" value="GeoX" />
> <values start="-4604000" increment="8000" npts="1152" />
> </variable>
> <variable name="y" shape="y" type="double">
> <attribute name="units" type="String" value="m" />
> <attribute name="_CoordinateAxisType" type="String" value="GeoY" />
> <values start="4604000" increment="8000" npts="1152" />
> </variable>
> <variable name="Projection" type="char">
> <attribute name="Projection_Name" type="String" 
> value="albers_conical_equal_area" />
> <attribute name="latitude_of_projection_origin" type="double" value="1" />
> <attribute name="longitude_of_central_meridian" type="double" value="20.0" />
> <attribute name="standard_parallel_1" type="double" value="21" />
> <attribute name="standard_parallel_2" type="double" value="-19" />
> <attribute name="false_easting" type="double" value="0" />
> <attribute name="false_northing" type="double" value="0" />
> <attribute name="_CoordinateTransformType" type="String" value="Projection" />
> <attribute name="_CoordinateAxes" type="String" value="x y" />
> <values />
> </variable>
> <variable name="NDVI" shape="T y x" type="double">
> <attribute name="long_name" type="String" value="normalized difference 
> vegetation index" />
> </variable>
> </netcdf>
> 
> I got the projection details from the IRI web catalog:
> 
> http://iridl.ldeo.columbia.edu/SOURCES/.USGS/.ADDS/.NDVI/.NDVIrg/.dekadal/.maximum/.NDVI/
> 
> Now, IDV still complains "No gridded data found for:". Should i try and use 
> the netCDF version of this?
> 
> http://iridl.ldeo.columbia.edu/SOURCES/.USGS/.ADDS/.NDVI/.NDVIrg/.dekadal/.maximum/.NDVI/data.cdf
> 
> Or should the ncml enhancements also work on an OpenDAP data pointer?

Your XML needed some tweaks:

For the projection:

- need to use standard_parallel with 2 values instead of _1 and _2
- the CoordinateAxes needs to be:

    <attribute name="_CoordinateAxisTypes" type="String" value="GeoX GeoY" />

- the attribute Projection_Name needs to be grid_mapping_name

For the variable NVDI, you need to indicate that it uses the particular 
projection:

  <variable name="NDVI" shape="T y x" type="double">
    <attribute name="long_name" type="String" value="normalized difference 
vegetation index" />
    <attribute name="grid_mapping" value="Projection"/>
  </variable>

Since this is following the CF-1.0 convention for the geolocation info, you
need a global attribute:

  <attribute name="Conventions" type="String" value="CF-1.0" />

to specify that convention.

The y axis needs to have a negative increment since it starts in the upper
left corner.

The ammended ncml file is attached.  Let me know if you have other
questions on this.

Don






Ticket Details
===================
Ticket ID: FAY-719487
Department: Support IDV
Priority: Normal
Status: Open

Attachment: test.ncml
Description: Binary data